It is known in the art relating to two cycle diesel engines for use in locomotives and other applications to provide a turbosupercharger (turbocharger) having a rotor including both compressor and turbine wheels and connected with the engine crankshaft by a gear train for driving the turbine, i.e. the turbocharger rotor, at a fixed minimum speed ratio relative to the engine (crankshaft) rotational speed. It should be understood that reference to an operating condition of the turbine, as is common among those skilled in the art, also applies where appropriate to the complete rotor including both turbine and compressor wheels.
The gear train includes an overrunning clutch that allows the turbine to freewheel, i.e overrun the mechanical drive and be driven solely by exhaust gas energy, at speeds higher than those of the fixed ratio. This provides for supercharging of the engine cylinders at higher engine speeds and loads where the energy in the exhaust gas is adequate for exhaust sustained turbocharger operation.
In one line of well known current production two cycle diesel engines used for railway, marine, powerplant and industrial applications, a gear and exhaust driven turbocharger similar to those of U.S. Pat. Nos. 3,667,214 granted Jun. 6, 1972 and 4,719,818 granted Jan. 18, 1988 is provided for supplying scavenging and charging air to the engine air box for delivery through ports to the engine cylinders.
As used in railway road locomotive (as opposed to switcher) applications it is common to provide a throttle control having eight engine speed settings from idle to full speed. A load control system controls the load applied to the engine by an engine driven generator to normally provide predetermined engine power settings for each power throttle speed setting from 1 to 8. The power settings are preselected to match the engine output with a desired power curve within scavenging and charging air pressure levels provided by the turbocharger. In general, these increase with the engine and turbocharger speed, but the charging pressure or pressure ratio increases significantly when the exhaust gas energy becomes sufficient to drive the turbine above the mechanically driven speed. Above this point, the air flow and pressure available are controlled by the combustion fuel energy which is limited by the full rack injector fuel injection capacity and the ability of the charging air supplied to cleanly burn this fuel (without significant exhaust smoke).
Thus at the full engine speed and in throttle setting 7, the turbocharger operation is almost always fully exhaust sustained and the full power setting takes account of the high pressure level provided in the engine cylinders. At throttle setting 6, ambient conditions of temperature, pressure, etc. may allow free wheeling (exhaust sustained) operation and, at lower throttle settings, the turbocharger operates at the speed determined by the mechanical drive ratio. The engine load at these lower throttle settings is substantially derated by matching fuel input to the limited charging air available during mechanically driven turbocharger operation and by the necessity of avoiding smoke during engine acceleration from lower to higher throttle settings.